Light emitting diodes (LEDs) are semiconductor chips that convert electrical energy directly into light, which use much less power and last much longer than incandescent lights. Since LEDs are efficient, give off little heat, and can be embedded in plastic and other durable materials, they are becoming more and more popular and may be used increasingly in the future not only for a wide range of signal and sign applications, but also for illumination applications. Early versions of LED technology had very low light output and were used primarily for indicator lights on electronic equipment. During the 1990s, however, industry developed brighter LEDs that are suitable for use in traffic and railroad signals, exit signs, and automobile turn and brake signals. Especially, after a first white LED has been developed at 1996 by coating a yellowish phosphor on a blue LED, LED lighting is gradually making great strides in power and efficiency and will play a more major role in general lighting. That is, LEDs are bundled together to provide adequate illumination and being used as the illumination module for applications, such as projectors, LCD-TV backlight modules, automobile head lights, and so on. However, there are still shortcomings preventing LED lighting from being commercially popularized, that the shortcoming includes insufficient luminous efficacy, difficult to dissipate heat and high cost, etc. Take the application of using LED module as automobile head light for example, although it is an appearing idea with great potential, currently LED head lights are only realized for those future car being demonstrated at auto shows. Until recently, though, the price of an LED lighting system was too high for most residential use. Nevertheless, with sales rising and more relating patents to be authorized, the price of high power LED illumination module is steadily decreasing. Therefore, for enabling the LED illumination module to be popularized, the problems, such as insufficient luminous efficacy and difficult to dissipate heat, must be resolved.
Most LED illumination modules bundle and package an array of serial/parallel-connected LEDs for satisfying the luminous flux required to form a high brightness LED illumination module. However, an LED illumination module with high luminous flux output usually accompany with high power requirement that is going to cause the LED illumination module to operate in a high temperature ambient while the exhaust heat can not be effectively discharged from the LED chip. If an LED illumination module is constantly operating in an environment of 120° C. or higher, the life span and luminous efficacy will be severely affected. Conventionally, the heat dissipating problem is solved by means similarly to those used for dissipating heat from center process unit (CPU), which includes the addition of heat dissipating fins, fans, or water-cooling system, etc., on the LED illumination module. But the additional cooling device will affect the structural simplicity and reliability of the LED illumination module, and more particularly, it will increase the cost of the LED illumination module.
In order to adapt LED illumination module to be used as light source of high brightness for projector or automobile, not only the brightness of LED illumination module must be increased, but also the overall volume of the LED illumination module must be reduced while increasing the luminous flux per unit light-emitting areas. Taking auto lamp for instance, a high intensity discharge (HID) head lamp three times as bright as a common halogen lamp, which is multiple times brighter than an LED can provide. Therefore, an LED illumination module, being adapted as auto lamp, must have a plurality of LEDs arranged therein so as to provide enough brightness equal to that of an HID head lamp. However, as the number of LEDs in a auto lamp increases, the size of the auto lamp must increase as well. According to an estimation made by auto lamp industry, there may be still five to ten years or longer before LED illumination modules can be used as head lamps. Hence, a compact, high brightness LED illumination module with high luminous flux per unit light-emitting area is desired.
Please refer to FIG. 1, which is a schematic view of a conventional high power LED projection lamp disclosed in T.W. Pat. No. M251074. The lamp 110 of FIG. 1 is mainly comprised of: a cup-like screen 111 made of conductive metal, having a connecting part with axially-bored hole 112 formed at the shrunken end of the screen, the screen further comprising a reflecting surface 113, disposed on the inner surface thereof, and a plurality of heat dissipating fins 114, formed on the exterior of the same; a base 120 with a plurality of metal legs; and a chip set 130, further comprising a plurality of LEDs. The lamp 110 of FIG. 1 is characterized in that the cup-like screen 110 is designed with function of light reflecting and heat dissipating, especially that the plural fins 114 added on the screen 111 can greatly increase the area of heat dissipation, and thus solve the heat dissipation problem troubling the conventional LED illumination modules. However, since the chip set 130 is limited to be disposed only on a planar surface, the amount of LEDs in the chip set 130 is limited and thus the luminous flux per unit light-emitting area can not be increased as require. Moreover, the arrangement of the plural heat dissipating fins 114 on the screen 111 will cause the overall volume of the lamp 110 to increase so that the dimensions of the lamp can not be reduced at will.
Please refer to FIG. 2, which is a schematic view of another conventional LED luminaire disclosed in T.W. Pat. No. I225713. The LED luminaire of FIG. 2 is substantially an integrated structure of an LED luminaire 23 and a heat pipe device. The heat pipe device is comprised of: an evaporator 236, having a volatile liquid received therein; and a condenser 237 with preferred thermal conductivity, connected and channeled to the evaporator 236. The LED luminaire 23 is comprised of: a base 230 having a plurality of LEDs 232 arranged therein; and a screen 234. Wherein, the evaporator 236 is connected to the base 230 while the condenser 237 is connected to the screen 234 so that the heat generated by the plural LEDs 232 can be transferred to the screen 234 by the cooperative operation of the evaporator 236 and the condenser 237, where the heat is distributed uniformly on the screen 234 and then to be discharged. As seen in FIG. 2, the stereo-designed base 230 arranged in the middle of the luminaire 23 allows the number of LEDs disposed therein to be increased at will, however, the vertically disposed LEDs 232 will cause the beams emitted thereby to be reflected by undesired angles that the luminous efficacy of the LED luminaire 23 is adversely affected. In addition, the heat pipe device adopted by the LED luminaire 23 will cause the fabrication cost of the same to increase.
Please refer to FIG. 3, which is a schematic view of yet another conventional LED luminaire disclosed in T.W. Pat. No. M248962. The LED luminaire 310 of FIG. 3 is composed of a plurality of light fixtures 311, each light fixture 311 further comprising a light collimating part 312 and a position part 313 having at least a substrate 330 fitted thereon for enabling a plurality of LEDs 331 to be fitted thereon; wherein the light collimating part 312 is disposed to reflect the light beams emitted from the plural LEDs 331 so as to enable the luminaire 310 to have comparatively better luminous efficacy. By the arrangement of the plural substrates 330, the number of LEDs to be arranged in the luminaire 310 can be increased at will and thus the luminous flux of the same is increased. However, the area of the luminaire 310 that can be used for heat dissipation is limited since the design of the luminaire 310 causes the heat generated thereby to be dissipated inwardly. Therefore, the working range of the operation power of the luminaire 310 is reduced.
From the above description, the shortcomings of those conventional LED illumination modules can be summed up as following:                (1) A single light-emitting surface limits the amount of LEDs to be disposed thereon that consequently limits the amount of luminous flux per unit light emitting area to be outputted.        (2) As the LEDs are concentrated on a single light-emitting surface, it is difficult to dissipate the exhaust heat generated thereby such that cause the LED illumination module to have poor heat dissipating efficiency.        (3) Most conventional LED illumination modules require addition heat dissipating device for dissipating exhaust heat, such as a heat pipe device. However, the addition of the heat pipe device generally will result the manufacturing cost of the LED illumination module to increase.        (4) Although the amount of LEDs fitted in an LED illumination module can be increased by arranging a plurality of outward-facing substrates for fitting LEDS thereon, the area of the LED illumination module that can be used for heat dissipation is reduced since the design will cause the heat generated thereby to be dissipated inwardly.        